The present invention relates to a scintillator. More specifically, the present invention relates to a LuxY(1−x)Xa3 scintillator for use, for example, in radiation detection, including gamma-ray spectroscopy and X-ray emission detection.
Scintillation spectrometers are widely used in detection and spectroscopy of energetic photons (e.g., X-rays and γ-rays). Such detectors are commonly used, for example, in nuclear and particle physics research, medical imaging, diffraction, non destructive testing, nuclear treaty verification and safeguards, nuclear non-proliferation monitoring, and geological exploration (Knoll Radiation Detection and Measurement, 3rd Edition, John Wiley and Sons, New York, (1999), Kleinknecht, Detectors for Particle Radiation, 2nd Edition, Cambridge University Press, Cambridge, U.K. (1998)).
Some important requirements for the scintillation materials used in these applications include, for example, high light output, transparency to the light it produces, high stopping efficiency, fast response, good proportionality, low cost and availability in large volume. Unfortunately, many of these requirements cannot be met by any of the commercially available scintillators.
Some commonly used scintillator materials include thallium-activated sodium iodide (NaI(Tl)), bismuth germanate (BGO), cerium-doped gadolinium orthosilicate (GSO), and cerium-doped lutetium orthosilicate (LSO). While these known scintillator materials do have some desirable scintillation characteristics which make them suitable for certain applications, each of the materials possesses one or more deficiencies that limit their use in a variety of applications. For example, many currently available scintillation materials have low light output characteristics, poor timing resolution (e.g., slow decay time or rise time), or low X-ray or gamma-ray stopping power. Some available materials also have emission spectra not optimally matched for use with certain commonly available photodetectors or have limited temperature ranges at which scintillation is practical or possible. In some instances, utility of certain available scintillators is limited due, for example, to absorption of oxygen and moisture leading to persistent afterglow and high background rate due to radioactive isotope of component elements.
While candidate scintillators or general classes of chemical compositions may be known or may even be identified as potentially having some scintillation characteristic(s), specific compositions/formulations having both scintillation characteristics and physical properties necessary for actual use in scintillation spectrometers and various practical applications have proven difficult to predict. Specific scintillation properties are not necessarily predictable from chemical composition alone, and preparing effective scintillators from even candidate materials often proves difficult. For example, while the composition of sodium chloride had been known for many years, the invention by Hofstadter of a high light-yield and conversion efficiency scintillator from sodium iodide doped with thallium launched the era of modern radiation spectrometry. More than half a century later, thallium doped sodium iodide, in fact, still remains one of the most widely used scintillator materials. Since the invention of NaI(Tl) scintillators in the 1940's, for half a century radiation detection applications have depended to a significant extent on this material. The fields of nuclear medicine, radiation monitoring and spectroscopy have grown up supported by NaI(Tl). Although far from ideal, NaI(Tl) was relatively easy to produce for a reasonable cost and in large volume. With the advent of X-ray CT in the 1970's, a major commercial field emerged as did a need for different scintillators, as NaI(Tl) was not able to meet the requirements of CT imaging. Later, the commercialization of PET imaging provided the impetus for the development of yet another class of detector materials with properties suitable for PET. As the methodology of scintillator development evolved, new materials have been added, and yet, specific applications are still hampered by the lack of scintillators suitable for particular applications.
As a result, there is continued interest in the search for new scintillators and formulations with both the enhanced performance and the physical characteristics needed for use in various applications (Derenzo, in, Heavy Scintillators for Scientific and Industrial Applications, De Notaristefani et al. eds., Gif-sur-Yvette, France (1993), pp. 125-135; van Eijk, Lecoq, Proc. Int. Conf. Inorganic Scintill. Appl., pps. 3-12, Shanghai, China, (1997); Moses, Nucl. Inst. Meth. A-487: 123-128 (2002)). Today, the development of new scintillators continues to be as much an art as a science, since the composition of a given material does not necessarily determine its properties as a scintillator, which are strongly influenced by the history (e.g., fabrication process) of the material as it is formed. While it is may be possible to reject a potential scintillator for a specific application based solely on composition, it is not possible to predict whether a material with promising composition will produce a scintillator with the desired properties.
Thus, a need exists for improved scintillator compositions suitable for use in various radiation detection applications. In particular, new scintillator materials are needed that can be efficiently and economically produced and that exhibit characteristics which enhance radiation detection, including, for example, high light output, high stopping efficiency, fast response, good proportionality, and minimal afterglow.